Intermediate unit for refrigeration apparatus, and refrigeration apparatus

ABSTRACT

An intermediate unit includes a liquid-side pipe, a first valve, and a refrigerant pressure sensor. The liquid-side pipe is connected to a liquid connection pipe connecting a heat source unit and a utilization unit together. A controller of the intermediate unit adjusts the opening degree of the first valve based on a value measured by the refrigerant pressure sensor. The pressure of a refrigerant to be sent through the liquid connection pipe from the intermediate unit to the utilization unit is adjusted by the first valve.

TECHNICAL FIELD

The present disclosure relates to an intermediate unit for arefrigeration apparatus and a refrigeration apparatus.

BACKGROUND ART

Patent Document 1 discloses a heat source unit forming part of arefrigeration apparatus. This heat source unit is connected through aconnection pipe to a show case or any other suitable object, which is autilization unit, and circulates a refrigerant between the heat sourceunit and the utilization unit to perform a refrigeration cycle.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2017-138034

SUMMARY

A first aspect of the present disclosure is directed to an intermediateunit (80) for a refrigeration apparatus (1). The intermediate unit (80)is provided between a heat source unit (10) and a utilization unit (60).The heat source unit (10) and the utilization unit (60) are connectedtogether through a liquid connection pipe (4) and a gas connection pipe(5) to form the refrigeration apparatus (1). The intermediate unit (80)includes: a liquid-side pipe (81) connected to the liquid connectionpipe (4); a first valve (18) provided for the liquid-side pipe (81), thefirst valve (18) having a variable opening degree; a refrigerantpressure sensor (48) disposed in a portion of the liquid-side pipe (81)closer to the utilization unit (60) than the first valve (18) is, therefrigerant pressure sensor (48) being configured to measure a pressureof a refrigerant flowing through the liquid-side pipe (81); and acontroller (85) configured to adjust the opening degree of the firstvalve (18) based on a value measured by the refrigerant pressure sensor(48).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping system diagram illustrating a configuration of arefrigeration apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating the relationship amongcontrollers, a sensor, and components of a refrigerant circuit.

FIG. 3 corresponds to FIG. 1 and illustrates a flow of a refrigerantthrough the refrigerant circuit during a cooling operation.

FIG. 4 corresponds to FIG. 1 and illustrates a flow of the refrigerantthrough the refrigerant circuit during a heating operation.

FIG. 5 corresponds to FIG. 1 and illustrates the state of therefrigerant circuit observed while refrigeration-facility units are in acooling-suspended state.

FIG. 6 is a flowchart showing how a hydraulic pressure controller of anembodiment operates to control a first valve.

FIG. 7 is a graph showing the relationship between the opening degree ofa second valve controlled by the hydraulic pressure controller of theembodiment and a value Pk measured by a refrigerant pressure sensor.

FIG. 8 is a graph showing the relationship between the opening degree ofa second valve controlled by a hydraulic pressure controller of avariation of the embodiment and a value Pk measured by a refrigerantpressure sensor.

FIG. 9 is a block diagram illustrating the relationship betweencomponents of an intermediate unit and a hydraulic pressure controller.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described below with reference to the drawings. Theembodiments below are merely exemplary ones in nature, and are notintended to limit the scope, applications, or use of the invention.

A refrigeration apparatus (1) of an embodiment can cool an object to becooled, and can condition indoor air. The object to be cooled hereinincludes air in facilities such as a refrigerator, a freezer, and a showcase. Hereinafter, such facilities are each referred to as arefrigeration-facility.

—General Configuration of Refrigeration Apparatus—

As illustrated in FIG. 1, the refrigeration apparatus (1) includes aheat source unit (10) installed outdoors, a plurality ofair-conditioning units (50) configured to condition indoor air, aplurality of refrigeration-facility units (60) configured to cool air ina refrigeration-facility, an intermediate unit (80), and a maincontroller (100). In the refrigeration apparatus (1) of the presentembodiment, the number of the heat source unit (10) is one, the numberof the refrigeration-facility units (60) is two or more, and the numberof the air-conditioning units (50) is two or more. Note that the numberof the refrigeration-facility units (60) or the air-conditioning units(50) of the refrigeration apparatus (1) may be one.

In the refrigeration apparatus (1), the heat source unit (10), therefrigeration-facility units (60), the air-conditioning units (50), theintermediate unit (80), and connection pipes (2, 3, 4, 5) connectingthese units (10, 50, 60, 80) together form a refrigerant circuit (6).

In the refrigerant circuit (6), a refrigerant circulates to perform arefrigeration cycle. The refrigerant in the refrigerant circuit (6) ofthe present embodiment is carbon dioxide. The refrigerant circuit (6) isconfigured to perform the refrigeration cycle so that the refrigeranthas a pressure equal to or greater than the critical pressure.

In the refrigerant circuit (6), the plurality of air-conditioning units(50) are connected through a first liquid connection pipe (2) and afirst gas connection pipe (3) to the heat source unit (10). In therefrigerant circuit (6), the plurality of air-conditioning units (50)are connected together in parallel.

In the refrigerant circuit (6), the plurality of refrigeration-facilityunits (60) are connected through a second liquid connection pipe (4) anda second gas connection pipe (5) to the heat source unit (10). In therefrigerant circuit (6), the plurality of refrigeration-facility units(60) are connected together in parallel.

In the refrigerant circuit (6), the intermediate unit (80) is connectedto the second liquid connection pipe (4) and the second gas connectionpipe (5) that connect the heat source unit (10) and therefrigeration-facility units (60) together. In other words, theintermediate unit (80) is disposed between the heat source unit (10) andthe refrigeration-facility units (60) in the refrigerant circuit (6).

The second liquid connection pipe (4) includes one first liquid-sidetrunk pipe (4 a), one second liquid-side trunk pipe (4 b), andliquid-side branch pipes (4 c) equal in number to therefrigeration-facility units (60). The first liquid-side trunk pipe (4a) is provided for a portion of the intermediate unit (80) near the heatsource unit (10). The second liquid-side trunk pipe (4 b) is providedfor a portion of the intermediate unit (80) near therefrigeration-facility units (60).

Specifically, the first liquid-side trunk pipe (4 a) connects the heatsource unit (10) and the intermediate unit (80) together. One end of thesecond liquid-side trunk pipe (4 b) is connected to the intermediateunit (80). The other end of the second liquid-side trunk pipe (4 b) isconnected to one end of each liquid-side branch pipe (4 c). The otherend of each liquid-side branch pipe (4 c) is connected to an associatedone of the refrigeration-facility units (60).

The second gas connection pipe (5) includes one first gas-side trunkpipe (5 a), one second gas-side trunk pipe (5 b), and gas-side branchpipes (5 c) equal in number to the refrigeration-facility units (60).The first gas-side trunk pipe (5 a) is provided for the portion of theintermediate unit (80) near the heat source unit (10). The secondgas-side trunk pipe (5 b) is provided for the portion of theintermediate unit (80) near the refrigeration-facility units (60).

Specifically, the first gas-side trunk pipe (5 a) connects the heatsource unit (10) and the intermediate unit (80) together. One end of thesecond gas-side trunk pipe (5 b) is connected to the intermediate unit(80). The other end of the second gas-side branch pipe (5 b) isconnected to one end of each gas-side branch pipe (5 c). The other endof each gas-side branch pipe (5 c) is connected to an associated one ofthe refrigeration-facility units (60).

—Heat Source Unit—

The heat source unit (10) includes an outdoor fan (12) and an outdoorcircuit (11). The outdoor circuit (11) includes a compression element(C), a flow path switching mechanism (30), an outdoor heat exchanger(13), an outdoor expansion valve (14), a gas-liquid separator (15), asubcooling heat exchanger (16), and an intercooler (17). The heat sourceunit (10) further includes an outdoor controller (101).

<Compression Element>

The compression element (C) compresses the refrigerant. The compressionelement (C) includes a first compressor (21), a second compressor (22),and a third compressor (23). The first, second, and third compressors(21), (22), and (23) are each a rotary compressor in which a motordrives a compression mechanism. The first, second, and third compressors(21), (22), and (23) are each configured as a variable capacitycompressor capable of changing the rotational speed of the compressionmechanism.

The compression element (C) performs two-stage compression. The firstcompressor (21) that is a high-stage compressor constitutes a firstcompression section. The second and third compressors (22) and (23) thatare low-stage compressors constitute a second compression section.

A first suction pipe (21 a) and a first discharge pipe (21 b) areconnected to the first compressor (21). A second suction pipe (22 a) anda second discharge pipe (22 b) are connected to the second compressor(22). A third suction pipe (23 a) and a third discharge pipe (23 b) areconnected to the third compressor (23). In the compression element (C),the second and third discharge pipes (22 b) and (23 b) are connected tothe first suction pipe (21 a).

The second suction pipe (22 a) is connected through a pipe to the firstgas-side trunk pipe (5 a) of the second gas connection pipe (5). Thesecond compressor (22) communicates with the refrigeration-facilityunits (60) through the second gas connection pipe (5). The secondcompressor (22) is a refrigeration-facility compressor associated withthe refrigeration-facility units (60). The third suction pipe (23 a)communicates with the air-conditioning units (50). The third compressor(23) is an indoor-side compressor associated with the air-conditioningunits (50).

The compression element (C) includes a second bypass pipe (24 b) and athird bypass pipe (24 c). The second bypass pipe (24 b) is a pipethrough which the refrigerant is passed while bypassing the secondcompressor (22). The second bypass pipe (24 b) has two ends respectivelyconnected to the second suction pipe (22 a) and the second dischargepipe (22 b). The third bypass pipe (24 c) is a pipe through which therefrigerant is passed while bypassing the third compressor (23). Thethird bypass pipe (24 c) has two ends respectively connected to thethird suction pipe (23 a) and the third discharge pipe (23 b).

<Flow Path Switching Mechanism>

The flow path switching mechanism (30) selects one of paths throughwhich the refrigerant flows in the refrigerant circuit (6). The flowpath switching mechanism (30) includes a first pipe (31), a second pipe(32), a third pipe (33), a fourth pipe (34), a first three-way valve(TV1), and a second three-way valve (TV2). The inflow end of the firstpipe (31) and the inflow end of the second pipe (32) are connected tothe first discharge pipe (21 b). The first pipe (31) and the second pipe(32) are pipes on which the discharge pressure of the compressionelement (C) acts. The outflow end of the third pipe (33) and the outflowend of the fourth pipe (34) are connected to the third suction pipe (23a) of the third compressor (23). The third pipe (33) and the fourth pipe(34) are pipes on which the suction pressure of the compression element(C) acts.

The first three-way valve (TV1) has a first port (P1), a second port(P2), and a third port (P3). The first port (P1) of the first three-wayvalve (TV1) is connected to the outflow end of the first pipe (31) thatis a high-pressure flow path. The second port (P2) of the firstthree-way valve (TV1) is connected to the inflow end of the third pipe(33) that is a low-pressure flow path. The third port (P3) of the firstthree-way valve (TV1) is connected to one end of an indoor gas-side flowpath (35). The other end of the indoor gas-side flow path (35) isconnected to the first gas connection pipe (3).

The second three-way valve (TV2) has a first port (P1), a second port(P2), and a third port (P3). The first port (P1) of the second three-wayvalve (TV2) is connected to the outflow end of the second pipe (32) thatis a high-pressure flow path. The second port (P2) of the secondthree-way valve (TV2) is connected to the inflow end of the fourth pipe(34) that is a low-pressure flow path. The third port (P3) of the secondthree-way valve (TV2) is connected to an outdoor gas-side flow path(36).

The first three-way valve (TV1) and the second three-way valve (TV2) areeach an electric three-way valve. The three-way valves (TV1, TV2) areeach switched between the first state (the state indicated by a solidline in FIG. 1) and the second state (the state indicated by a dashedline in FIG. 1). In the three-way valves (TV1, TV2) in the first state,the first port (P1) and the third port (P3) communicate with each other,and the second port (P2) is closed. In the three-way valves (TV1, TV2)in the second state, the second port (P2) and the third port (P3)communicate with each other, and the first port (P1) is closed.

<Outdoor Heat Exchanger>

The outdoor heat exchanger (13) constitutes a heat-source-side heatexchanger. The outdoor heat exchanger (13) is a fin-and-tube air heatexchanger. The outdoor fan (12) is disposed near the outdoor heatexchanger (13). The outdoor fan (12) transfers outdoor air. The outdoorheat exchanger exchanges heat between a refrigerant flowing therethroughand outdoor air transferred from the outdoor fan (12).

The gas end of the outdoor heat exchanger (13) is connected to theoutdoor gas-side flow path (36). The liquid end of the outdoor heatexchanger (13) is connected to an outdoor flow path (O).

<Outdoor Flow Path>

The outdoor flow path (O) includes a first outdoor pipe (o1), a secondoutdoor pipe (o2), a third outdoor pipe (o3), a fourth outdoor pipe(o4), a fifth outdoor pipe (o5), a sixth outdoor pipe (o6), a seventhoutdoor pipe (o7), and an eighth outdoor pipe (o8).

One end of the first outdoor pipe (o1) is connected to the liquid end ofthe outdoor heat exchanger (13). The other end of the first outdoor pipe(o1) is connected to one end of the second outdoor pipe (o2) and one endof the third outdoor pipe (o3). The other end of the second outdoor pipe(o2) is connected to the top of the gas-liquid separator (15).

One end of the fourth outdoor pipe (o4) is connected to the bottom ofthe gas-liquid separator (15). The other end of the fourth outdoor pipe(o4) is connected to one end of the fifth outdoor pipe (o5) and theother end of the third outdoor pipe (o3). The other end of the fifthoutdoor pipe (o5) is connected to one end of the sixth outdoor pipe (o6)and one end of the eighth outdoor pipe (o8).

The other end of the eighth outdoor pipe (o8) is connected to the firstliquid-side trunk pipe (4 a) of the second liquid connection pipe (4).The eighth outdoor pipe (o8) is a liquid pipe through which a liquidrefrigerant downstream of the gas-liquid separator (15) flows. The otherend of the sixth outdoor pipe (o6) is connected to the first liquidconnection pipe (2). One end of the seventh outdoor pipe (o7) isconnected to an intermediate portion of the sixth outdoor pipe (o6). Theother end of the seventh outdoor pipe (o7) is connected to anintermediate portion of the second outdoor pipe (o2).

<Outdoor Expansion Valve>

The first outdoor pipe (o1) of the outdoor circuit (11) is provided withan outdoor expansion valve (14). The outdoor expansion valve (14) is anelectronic expansion valve that has its opening degree adjusted by apulse motor driven in response to a pulse signal from the maincontroller (100).

<Gas-Liquid Separator>

The gas-liquid separator (15) constitutes a container that stores therefrigerant. The gas-liquid separator (15) is provided downstream of theoutdoor expansion valve (14). In the gas-liquid separator (15), therefrigerant is separated into a gas refrigerant and a liquidrefrigerant. The top of the gas-liquid separator (15) is connected tothe other end of the second outdoor pipe (o2) and one end of a ventingpipe (37), which will be described below.

<Intermediate Injection Circuit>

The outdoor circuit (11) includes an intermediate injection circuit(49). The intermediate injection circuit (49) is a circuit through whichthe refrigerant decompressed by a decompression valve (40) is suppliedto an intermediate pressure section of the compression element (C)between the first compression section (21) and the second compressionsection (22, 23). The intermediate injection circuit (49) includes theventing pipe (37) and an injection pipe (38).

One end of the injection pipe (38) is connected to an intermediateportion of the fifth outdoor pipe (o5). The other end of the injectionpipe (38) is connected to the first suction pipe (21 a) of the firstcompressor (21). The injection pipe (38) is provided with thedecompression valve (40). The decompression valve (40) is an expansionvalve having a variable opening degree.

The venting pipe (37) is configured to allow the gas refrigerant in thegas-liquid separator (15) to flow out of the gas-liquid separator (15)into a flow path between the first compression section (21) and thesecond compression section (22, 23). Specifically, one end of theventing pipe (37) is connected to the top of the gas-liquid separator(15). The other end of the venting pipe (37) is connected to anintermediate portion of the injection pipe (38). The venting pipe (37)is connected to a venting valve (39). The venting valve (39) is anelectronic expansion valve having a variable opening degree.

<Subcooling Heat Exchanger>

The outdoor circuit (11) includes the subcooling heat exchanger (16).The subcooling heat exchanger (16) is a cooling heat exchangerconfigured to cool the refrigerant (mainly the liquid refrigerant)separated in the gas-liquid separator (15). The subcooling heatexchanger (16) is connected between the gas-liquid separator (15) and afirst valve (18). The subcooling heat exchanger (16) has a first flowpath (16 a) serving as a high-pressure flow path and a second flow path(16 b) serving as a low-pressure flow path. In the subcooling heatexchanger (16), heat exchange occurs between the high-pressurerefrigerant flowing through the first flow path (16 a) and thedecompressed refrigerant flowing through the second flow path (16 b).

The refrigerant flowing through the first flow path (16 a) is cooled inthe subcooling heat exchanger (16). The first flow path (16 a) isconnected to an intermediate portion of the fourth outdoor pipe (o4)serving as a liquid pipe through which the liquid refrigerant in theoutdoor circuit (11) flows.

The second flow path (16 b) is a flow path through which the refrigerantserving to cool the refrigerant flowing through the first flow path (16a) flows. The second flow path (16 b) is included in the intermediateinjection circuit (49). Specifically, the second flow path (16 b) isconnected to a portion of the injection pipe (38) downstream of thedecompression valve (40). The refrigerant that has been decompressed atthe decompression valve (40) flows through the second flow path (16 b).

<Intercooler>

The intercooler (17) is connected to an intermediate flow path (41). Oneend of the intermediate flow path (41) is connected to the seconddischarge pipe (22 b) of the second compressor (22) and the thirddischarge pipe (23 b) of the third compressor (23). The other end of theintermediate flow path (41) is connected to the first suction pipe (21a) of the first compressor (21). In other words, the other end of theintermediate flow path (41) is connected to the intermediate pressuresection of the compression element (C).

The intercooler (17) is a fin-and-tube air heat exchanger. A cooling fan(17 a) is disposed near the intercooler (17). The intercooler (17)exchanges heat between the refrigerant flowing therethrough and theoutdoor air transferred from the cooling fan (17 a).

<Oil Separation Circuit>

The outdoor circuit (11) includes an oil separation circuit (42). Theoil separation circuit (42) includes an oil separator (43), a first oilreturn pipe (44), a second oil return pipe (45), and a third oil returnpipe (46).

The oil separator (43) is connected to the first discharge pipe (21 b)of the first compressor (21). The oil separator (43) separates oil fromthe refrigerant discharged from the compression element (C).

The inflow end of the first oil return pipe (44) communicates with theoil separator (43). The outflow end of the first oil return pipe (44) isconnected to the second suction pipe (22 a) of the second compressor(22). The inflow end of the second oil return pipe (45) communicateswith the oil separator (43). The outflow end of the second oil returnpipe (45) is connected to the inflow end of the intermediate flow path(41).

The third oil return pipe (46) includes a main return pipe (46 a), arefrigeration-facility-side branch pipe (46 b), and an indoor-sidebranch pipe (46 c). The inflow end of the main return pipe (46 a)communicates with the oil separator (43). The outflow end of the mainreturn pipe (46 a) is connected to the inflow end of therefrigeration-facility-side branch pipe (46 b) and the inflow end of theindoor-side branch pipe (46 c). The outflow end of therefrigeration-facility-side branch pipe (46 b) communicates with an oilreservoir inside a casing of the second compressor (22). The outflow endof the indoor-side branch pipe (46 c) communicates with an oil reservoirinside a casing of the third compressor (23).

The first oil return pipe (44) is connected to a first oil level controlvalve (47 a). The second oil return pipe (45) is connected to a secondoil level control valve (47 b). The refrigeration-facility-side branchpipe (46 b) is connected to a third oil level control valve (47 c). Theindoor-side branch pipe (46 c) is connected to a fourth oil levelcontrol valve (47 d).

A portion of oil separated in the oil separator (43) returns to thesecond compressor (22) via the first oil return pipe (44). Anotherportion of the oil separated in the oil separator (43) returns to thethird compressor (23) via the second oil return pipe (45). The remainingportion of the oil separated in the oil separator (43) returns to theoil reservoir in the casing of each of the second compressor (22) andthe third compressor (23) via the third oil return pipe (46).

<Check Valve>

The outdoor circuit (11) has a first check valve (CV1), a second checkvalve (CV2), a third check valve (CV3), a fourth check valve (CV4), afifth check valve (CV5), a sixth check valve (CV6), a seventh checkvalve (CV7), an eighth check valve (CV8), and a ninth check valve (CV9).Each of these check valves (CV1 to CV9) allows the refrigerant to flowin the direction of the associated arrow shown in FIG. 1 and prohibitsthe refrigerant to flow in the opposite direction.

The first check valve (CV1) is connected to the first discharge pipe (21b). The second check valve (CV2) is connected to the second dischargepipe (22 b). The third check valve (CV3) is connected to the thirddischarge pipe (23 b). The fourth check valve (CV4) is connected to thesecond outdoor pipe (o2). The fifth check valve (CV5) is connected tothe third outdoor pipe (o3). The sixth check valve (CV6) is connected tothe sixth outdoor pipe (o6). The seventh check valve (CV7) is connectedto the seventh outdoor pipe (o7). The eighth check valve (CV8) isconnected to the second bypass pipe (24 b). The ninth check valve (CV9)is connected to the third bypass pipe (24 c).

<Sensor>

The heat source unit (10) includes various sensors. The sensors includea high-pressure sensor (71), an intermediate-pressure sensor (72), afirst low-pressure sensor (73), a second low-pressure sensor (74), and aliquid refrigerant pressure sensor (75).

The high-pressure sensor (71) detects the pressure of the refrigerant(the pressure (HP) of a high-pressure refrigerant) discharged from thefirst compressor (21). The intermediate-pressure sensor (72) detects thepressure of the refrigerant in the intermediate flow path (41), i.e.,the pressure of the refrigerant between the first compressor (21) and apair of the second and third compressors (22) and (23) (the pressure(MP) of an intermediate-pressure refrigerant). The first low-pressuresensor (73) detects the pressure of the refrigerant (the pressure (LP1)of a first low-pressure refrigerant) to be sucked by the secondcompressor (22). The second low-pressure sensor (74) detects thepressure of the refrigerant (the pressure (LP2) of a second low-pressurerefrigerant) to be sucked by the third compressor (23). The liquidrefrigerant pressure sensor (75) detects the pressure of the liquidrefrigerant (the pressure (RP) of the liquid refrigerant) in thegas-liquid separator (15).

—Air-Conditioning Unit—

The air-conditioning units (50) are utilization units installed indoors.The air-conditioning units (50) each condition air in an indoor space.The air-conditioning units (50) each include an indoor fan (52) and anindoor circuit (51). The liquid end of the indoor circuit (51) isconnected to the first liquid connection pipe (2). The gas end of theindoor circuit (51) is connected to the first gas connection pipe (3).

The indoor circuit (51) includes an indoor expansion valve (53) and anindoor heat exchanger (54) in order from the liquid end to the gas end.The indoor expansion valve (53) is a first utilization expansion valve.The indoor expansion valve (53) is an electronic expansion valve havinga variable opening degree.

The indoor heat exchanger (54) is a fin-and-tube air heat exchanger. Theindoor fan (52) is disposed near the indoor heat exchanger (54). Theindoor fan (52) transfers indoor air. The indoor heat exchanger (54)exchanges heat between a refrigerant flowing therethrough and indoor airtransferred from the indoor fan (52).

The air-conditioning units (50) each include an indoor controller (102).Although not shown, the air-conditioning units (50) each include aplurality of temperature sensors. The temperature sensors of eachair-conditioning unit (50) include a sensor configured to measure thetemperature of indoor air and a sensor configured to measure thetemperature of the refrigerant flowing through the indoor circuit (51).

—Main Controller—

As illustrated in FIG. 2, the main controller (100) includes an outdoorcontroller (101) for the heat source unit (10) and the indoorcontrollers (102) for the respective air-conditioning units (50). Theoutdoor controller (101) and each of the indoor controllers (102)forming the main controller (100) are connected together through acommunication line to be capable of communicating with each other.

The outdoor controller (101) and the indoor controllers (102) eachinclude a microcomputer mounted on a control board, and a memory device(specifically, a semiconductor memory) storing software for operatingthe microcomputer. The main controller (100) controls various componentsof the refrigeration apparatus (1) based on detection signals of thevarious sensors.

The outdoor controller (101) controls the compression element (C) sothat a value measured by the high-pressure sensor (71) (the pressure(HP) of the high-pressure refrigerant) is greater than or equal to thecritical pressure of the refrigerant (in the present embodiment, carbondioxide). The outdoor controller (101) controls the outdoor expansionvalve (14) so that the refrigerant pressure in the gas-liquid separator(15) (specifically, a value measured by the liquid refrigerant pressuresensor (75)) is less than the critical pressure of the refrigerant.

The outdoor controller (101) controls the cooling capability of thesubcooling heat exchanger (16). Specifically, the outdoor controller(101) controls the decompression valve (40) so that the refrigerantflowing out of the subcooling heat exchanger (16) is subcooled.

The indoor controllers (102) each control the operation of theassociated air-conditioning unit (50) so that the temperature of airsucked into the associated air-conditioning unit (50) becomes equal to aset temperature. Specifically, the indoor controllers (102) each controlthe associated indoor expansion valve (53) and the associated indoor fan(52).

—Refrigeration-Facility Unit—

The refrigeration-facility units (60) are each, for example, arefrigerated show case installed in a store, such as a conveniencestore. Each refrigeration-facility unit (60) is a utilization unit thatis installed indoors to cool air in the show case (inside air). Therefrigeration-facility unit (60) includes a refrigeration-facility fan(62) and a refrigeration-facility circuit (61). The liquid end of therefrigeration-facility circuit (61) is connected to the associatedliquid-side branch pipe (4 c) of the second liquid connection pipe (4).The gas end of the refrigeration-facility circuit (61) is connected tothe associated gas-side branch pipe (5 c) of the second gas connectionpipe (5).

The refrigeration-facility circuit (61) includes arefrigeration-facility expansion valve (63) and a refrigeration-facilityheat exchanger (64) in order from the liquid end to the gas end. Therefrigeration-facility expansion valve (63) is configured as anelectronic expansion valve having a variable opening degree.

The refrigeration-facility heat exchanger (64) is a fin-and-tube airheat exchanger. The refrigeration-facility fan (62) is disposed near therefrigeration-facility heat exchanger (64). The refrigeration-facilityfan (62) transfers inside air. The refrigeration-facility heat exchanger(64) exchanges heat between the refrigerant flowing therethrough andinside air transferred from the refrigeration-facility fan (62).

The refrigeration-facility units (60) each include arefrigeration-facility controller (103). Although not shown, therefrigeration-facility units (60) each include a plurality oftemperature sensors. The temperature sensors of eachrefrigeration-facility unit (60) include a sensor configured to measurethe temperature of inside air and a sensor configured to measure thetemperature of the refrigerant flowing through therefrigeration-facility circuit (61).

As illustrated in FIG. 2, the refrigeration-facility controllers (103)each include a microcomputer mounted on a control board, and a memorydevice (specifically, a semiconductor memory) storing software foroperating the microcomputer. The refrigeration-facility controllers(103) do not communicate with the outdoor controller (101) and theindoor controllers (102).

Each refrigeration-facility controller (103) controls the associatedrefrigeration-facility expansion valve (63) and the associatedrefrigeration-facility fan (62) based on detection signals of thevarious sensors. The refrigeration-facility controller (103) adjusts theopening degree of the associated refrigeration-facility expansion valve(63) so that the degree of superheat of the refrigerant at the outlet ofthe associated refrigeration-facility heat exchanger (64) functioning asan evaporator becomes equal to a predetermined target value. If thetemperature of inside air falls within a set temperature range, therefrigeration-facility controller (103) allows a cooling operation ofthe associated refrigeration-facility unit (60) to be suspended. In thiscooling-suspended state, while the refrigeration-facility fan (62)operates, the refrigeration-facility expansion valve (63) is closed.

—Intermediate Unit—

The intermediate unit (80) is separate from the heat source unit (10),the air-conditioning units (50), and the refrigeration-facility units(60). The intermediate unit (80) includes a liquid-side pipe (81), agas-side pipe (82), and a joint pipe (83). Although not shown, theintermediate unit (80) includes a casing that houses the liquid-sidepipe (81), the gas-side pipe (82), and the joint pipe (83). Theintermediate unit (80) is installed indoors together with therefrigeration-facility units (60).

One end of the liquid-side pipe (81) is connected to the firstliquid-side trunk pipe (4 a) of the second liquid connection pipe (4),and the other end thereof is connected to the second liquid-side trunkpipe (4 b) of the second liquid connection pipe (4). As can be seen, theliquid-side pipe (81) is connected to the liquid-side trunk pipes (4 a,4 b) of the second liquid connection pipe (4) connecting the heat sourceunit (10) and the refrigeration-facility units (60) together.

The liquid-side pipe (81) is provided with the first valve (18) and arefrigerant pressure sensor (48) in order from the one end to the otherend thereof. Thus, the refrigerant pressure sensor (48) is disposed in aportion of the liquid-side pipe (81) closer to therefrigeration-facility units (60) than the first valve (18) is.

The first valve (18) is a control valve having a variable openingdegree. The first valve (18) of the present embodiment is an electronicexpansion valve including a pulse motor that drives its valve body. Therefrigerant pressure sensor (48) measures the pressure of therefrigerant flowing through the liquid-side pipe (81). A value measuredby the refrigerant pressure sensor (48) is substantially equal to thepressure of the refrigerant flowing through the liquid-side pipe (81)into the second liquid-side trunk pipe (4 b).

One end of the gas-side pipe (82) is connected to the first gas-sidetrunk pipe (5 a) of the second gas connection pipe (5), and the otherend thereof is connected to the second gas-side trunk pipe (5 b) of thesecond gas connection pipe (5). As can be seen, the gas-side pipe (82)is connected to the gas-side trunk pipes (5 a, 5 b) of the second gasconnection pipe (5) connecting the heat source unit (10) and therefrigeration-facility units (60) together.

One end of the joint pipe (83) is connected to the liquid-side pipe(81), and the other end thereof is connected to the gas-side pipe (82).The one end of the join pipe (83) is connected to a portion of theliquid-side pipe (81) closer to the second liquid-side trunk pipe (4 b)than the first valve (18) is. The one end of the join pipe (83) of thepresent embodiment is connected to a portion of the liquid-side pipe(81) closer to the second liquid-side trunk pipe (4 b) than therefrigerant pressure sensor (48) is. Note that the one end of the jointpipe (83) may be connected to a portion of the liquid-side pipe (81)between the first valve (18) and the refrigerant pressure sensor (48).

The joint pipe (83) is provided with a second valve (19). The secondvalve (19) is a control valve having a variable opening degree. Thesecond valve (19) of the present embodiment is an electronic expansionvalve including a pulse motor that drives its valve body.

The intermediate unit (80) includes a hydraulic pressure controller(85). The hydraulic pressure controller (85) is connected to the firstvalve (18), the second valve (19), and the refrigerant pressure sensor(48) via communication lines. The hydraulic pressure controller (85)controls the first and second valves (18) and (19) based on the valuemeasured by the refrigerant pressure sensor (48).

As illustrated in FIG. 2, the hydraulic pressure controller (85)includes a microcomputer mounted on a control board, and a memory device(specifically, a semiconductor memory) storing software for operatingthe microcomputer. The hydraulic pressure controller (85) does notcommunicate with the outdoor controller (101), the indoor controllers(102), and the refrigeration-facility controllers (103).

—Operation of Refrigeration Apparatus—

An operation of the refrigeration apparatus (1) will be described. Therefrigeration apparatus (1) can perform a cooling operation and aheating operation. The cooling operation is an operation in which theair-conditioning units (50) cool the respective indoor spaces. Theheating operation is an operation in which the air-conditioning units(50) heat the respective indoor spaces. In each of the cooling operationand the heating operation, the refrigeration-facility units (60) areeach either in an active state or in the cooling-suspended state.

<Cooling Operation>

The cooling operation of the refrigeration apparatus (1) will bedescribed with reference to FIG. 3. The cooling operation will behereinafter described using an example in which therefrigeration-facility units (60) are in the active state.

In the cooling operation illustrated in FIG. 3, the refrigerant circuit(6) allows the refrigerant to circulate therethrough to perform arefrigeration cycle. The outdoor heat exchanger (13) functions as aradiator (a gas cooler), and the refrigeration-facility heat exchangers(64) and the indoor heat exchangers (54) function as evaporators.

In the cooling operation illustrated in FIG. 3, the first three-wayvalve (TV1) is set in the second state, and the second three-way valve(TV2) is set in the first state. The outdoor expansion valve (14), therefrigeration-facility expansion valves (63), the indoor expansionvalves (53), the decompression valve (40), and the first valve (18) havetheir opening degrees adjusted as appropriate. The outdoor fan (12), thecooling fan (17 a), the refrigeration-facility fans (62), and the indoorfans (52) operate. The first, second, and third compressors (21), (22),and (23) operate.

The refrigerant that has been compressed in each of the second and thirdcompressors (22) and (23) dissipates heat to outdoor air in theintercooler (17), and is then sucked into the first compressor (21). Therefrigerant that has been compressed in the first compressor (21)dissipates heat to outdoor air in the outdoor heat exchanger (13), andis then decompressed while passing through the outdoor expansion valve(14). The decompressed refrigerant has a pressure that is lower than asecond pressure (critical pressure). This refrigerant passes through thegas-liquid separator (15), and is then cooled in the subcooling heatexchanger (16). A portion of the refrigerant that has been cooled in thesubcooling heat exchanger (16) flows into the eighth outdoor pipe (o8),and the remaining portion thereof flows into the sixth outdoor pipe(o6).

The refrigerant that has flowed into the sixth outdoor pipe (o6) flowsthrough the first liquid connection pipe (2), and is distributed amongthe plurality of air-conditioning units (50). In each air-conditioningunit (50), the refrigerant that has flowed into the indoor circuit (51)is decompressed while passing through the indoor expansion valve (53),and then absorbs heat from the indoor air to evaporate in the indoorheat exchanger (54). The air-conditioning unit (50) blows the air cooledin the indoor heat exchanger (54) into the indoor space. The flows ofthe refrigerant that has flowed out of the indoor heat exchangers (54)of the air-conditioning units (50) enter the first gas connection pipe(3) to merge together. Thereafter, this refrigerant flows into theoutdoor circuit (11), and is then sucked into the third compressor (23)so as to be again compressed.

The refrigerant that has flowed into the eighth outdoor pipe (o8) flowsthrough the first liquid-side trunk pipe (4 a) of the second liquidconnection pipe (4) into the liquid-side pipe (81) of the intermediateunit (80). The refrigerant that has flowed into the liquid-side pipe(81) is decompressed while passing through the first valve (18), thenpasses through the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) of the second liquid connection pipe (4),and is distributed among the plurality of refrigeration-facility units(60).

In each refrigeration-facility unit (60), the refrigerant that hasflowed into the refrigeration-facility circuit (61) is decompressedwhile passing through the refrigeration-facility expansion valve (63),and then absorbs heat from the inside air to evaporate in therefrigeration-facility heat exchanger (64). The refrigeration-facilityunit (60) blows the air cooled in the refrigeration-facility heatexchanger (64) into a space inside the refrigeration-facility.

The flows of the refrigerant that has flowed out of therefrigeration-facility heat exchangers (64) of therefrigeration-facility units (60) enter the second gas connection pipe(5) to merge together. Thereafter, this refrigerant flows into thegas-side pipe (82) of the intermediate unit (80), passes through thegas-side pipe (82), and then flows through the first gas-side trunk pipe(5 a) into the outdoor circuit (11). Thereafter, the refrigerant issucked into the second compressor (22) so as to be again compressed.

<Heating Operation>

The heating operation of the refrigeration apparatus (1) will bedescribed with reference to FIG. 4. The heating operation will behereinafter described using an example in which therefrigeration-facility units (60) are in the active state.

In the heating operation illustrated in FIG. 4, the refrigerant circuit(6) allows the refrigerant to circulate therethrough to perform arefrigeration cycle. The indoor heat exchangers (54) function asradiators (gas coolers), and the refrigeration-facility heat exchangers(64) and the outdoor heat exchanger (13) function as evaporators. Notethat, in the heating operation, the refrigeration apparatus (1) of thepresent embodiment is operable either in a mode in which the outdoorheat exchanger (13) functions as a radiator or in a mode in which theoutdoor heat exchanger (13) is suspended.

In the heating operation illustrated in FIG. 4, the first three-wayvalve (TV1) is set in the first state, and the second three-way valve(TV2) is set in the second state. The outdoor expansion valve (14), therefrigeration-facility expansion valves (63), the indoor expansionvalves (53), the decompression valve (40), and the first valve (18) havetheir opening degrees adjusted as appropriate. The outdoor fan (12), therefrigeration-facility fans (62), and the indoor fans (52) operate, andthe cooling fan (17 a) is suspended. The first, second, and thirdcompressors (21), (22), and (23) operate.

The refrigerant that has been compressed in each of the second and thirdcompressors (22) and (23) passes through the intercooler (17), and isthen sucked into the first compressor (21). The refrigerant that hasbeen compressed in the first compressor (21) flows through the first gasconnection pipe (3), and is distributed among the plurality ofair-conditioning units (50). In each air-conditioning unit (50), therefrigerant that has flowed into the indoor circuit (51) dissipates heatto the indoor air in the indoor heat exchanger (54), and then flows intothe first liquid connection pipe (2) after passing through the indoorexpansion valve (53). The air-conditioning unit (50) blows the airheated in the indoor heat exchanger (54) into the indoor space.

The flows of the refrigerant that has flowed out of the air-conditioningunits (50) into the first liquid connection pipe (2) merge together.Thereafter, this refrigerant flows through the seventh outdoor pipe (o7)of the outdoor circuit (11) into the gas-liquid separator (15), and isthen cooled in the subcooling heat exchanger (16). A portion of therefrigerant that has been cooled in the subcooling heat exchanger (16)flows into the fifth outdoor pipe (o5), and the remaining portionthereof flows into the third outdoor pipe (o3).

The refrigerant that has flowed into the fifth outdoor pipe (o5) thenflows through the eighth outdoor pipe (o8) and the first liquid-sidetrunk pipe (4 a) of the second liquid connection pipe (4) in this orderinto the liquid-side pipe (81) of the intermediate unit (80). Therefrigerant that has flowed into the liquid-side pipe (81) isdecompressed while passing through the first valve (18), then passesthrough the second liquid-side trunk pipe (4 b) and the liquid-sidebranch pipes (4 c) of the second liquid connection pipe (4), and isdistributed among the plurality of refrigeration-facility units (60).

In each refrigeration-facility unit (60), the refrigerant that hasflowed into the refrigeration-facility circuit (61) is decompressedwhile passing through the refrigeration-facility expansion valve (63),and then absorbs heat from the inside air to evaporate in therefrigeration-facility heat exchanger (64). The refrigeration-facilityunit (60) blows the air cooled in the refrigeration-facility heatexchanger (64) into a space inside the refrigeration-facility.

The flows of the refrigerant that has flowed out of therefrigeration-facility heat exchangers (64) of therefrigeration-facility units (60) enter the second gas connection pipe(5) to merge together. Thereafter, this refrigerant flows into thegas-side pipe (82) of the intermediate unit (80), passes through thegas-side pipe (82), and then flows through the first gas-side trunk pipe(5 a) into the outdoor circuit (11). Thereafter, the refrigerant issucked into the second compressor (22) so as to be again compressed.

The refrigerant that has flowed into the third outdoor pipe (o3) isdecompressed while passing through the outdoor expansion valve (14),then flows into the outdoor heat exchanger (13), and absorbs heat fromthe outdoor air to evaporate in the outdoor heat exchanger (13). Therefrigerant that has flowed out of the outdoor heat exchanger (13) issucked into the third compressor (23) so as to be again compressed.

<Cooling-Suspended State of Refrigeration-Facility Unit>

While there is no need to cool the inside air, the associatedrefrigeration-facility unit (60) is in the cooling-suspended state.Specifically, if the inside air sucked into each refrigeration-facilityunit (60) has a temperature that falls below the lower limit of apredetermined target range, the refrigeration-facility controller (103)of the refrigeration-facility unit (60) closes therefrigeration-facility expansion valve (63) to change the state of therefrigeration-facility unit (60) from the active state to thecooling-suspended state. In this cooling-suspended state, therefrigeration-facility fan (62) keeps operating. Therefrigeration-facility expansion valve (63) closed prevents therefrigerant from being supplied from the second liquid connection pipe(4) to the refrigeration-facility unit (60), thereby stopping thecooling of air in the refrigeration-facility heat exchanger (64).

If the inside air sucked into each refrigeration-facility unit (60) hasa temperature that exceeds the upper limit of the predetermined targetrange, the refrigeration-facility controller (103) opens therefrigeration-facility expansion valve (63) to change the state of therefrigeration-facility unit (60) from the cooling-suspended state to theactive state. If the state of the refrigeration-facility unit (60) ischanged from the cooling-suspended state to the active state, thecooling of air in the refrigeration-facility heat exchanger (64) isrestarted.

If all of the refrigeration-facility units (60) are in thecooling-suspended state during operation of the second compressor (22),the refrigerant pressure in the second gas connection pipe (5)decreases. As a result, a value measured by the first low-pressuresensor (73) decreases. If the value measured by the first low-pressuresensor (73) thus falls below a predetermined first reference value, theoutdoor controller (101) stops the second compressor (22).

If the state of at least one of the refrigeration-facility units (60) ischanged from the cooling-suspended state to the active state during thestop of the second compressor (22), the refrigerant pressure in thesecond gas connection pipe (5) increases. As a result, the valuemeasured by the first low-pressure sensor (73) increases. If the valuemeasured by the first low-pressure sensor (73) thus exceeds apredetermined second reference value, the outdoor controller (101)actuates the second compressor (22).

—Control Operation of Hydraulic Pressure Controller—

A control operation performed by the hydraulic pressure controller (85)of the intermediate unit (80) will be described.

The hydraulic pressure controller (85) controls the first and secondvalves (18) and (19) so that the refrigerant pressure in therefrigeration-facility circuit (61) of each refrigeration-facility unit(60) is kept at or below the refrigerant pressure that can be allowed bythe refrigeration-facility circuit (61). The refrigerant pressure thatcan be allowed by the refrigeration-facility circuit (61) is theallowable pressure Pu of the refrigeration-facility unit (60). Theallowable pressure Pu of the refrigeration-facility unit (60) of thepresent embodiment is 6 MPa (Pu=6 MPa). Note that the pressure valueused to describe the control operation of the hydraulic pressurecontroller (85) is merely an example.

Here, if each refrigeration-facility unit (60) is in the active state,the value measured by the refrigerant pressure sensor (48) is slightlyhigher than the pressure of the refrigerant at the inlet of therefrigeration-facility circuit (61). The reason for this is that therefrigerant has its pressure gradually reduced, while flowing throughthe second liquid-side trunk pipe (4 b) and the liquid-side branch pipe(4 c). Meanwhile, the hydraulic pressure controller (85) of the presentembodiment controls the opening degrees of the first and second valves(18) and (19) so that the value Pk measured by the refrigerant pressuresensor (48) is lower than the allowable pressure Pu of therefrigeration-facility units (60), as will be described below. Thus, thehydraulic pressure controller (85) controlling the first and secondvalves (18) and (19) allows the pressure of the refrigerant flowing intothe refrigeration-facility circuit (61) of each refrigeration-facilityunit (60) to be kept below the allowable pressure Pu of therefrigeration-facility unit (60).

<Control of First Valve>

An operation performed by the hydraulic pressure controller (85) tocontrol the opening degree of the first valve (18) will be describedwith reference to the flowchart shown in FIG. 6. The hydraulic pressurecontroller (85) repeatedly performs the control operation shown in theflowchart of FIG. 6 at predetermined time intervals (e.g., 30 seconds).

In the process performed in step ST1, the hydraulic pressure controller(85) reads the value Pk measured by the refrigerant pressure sensor(48), and compares the measured value Pk with a first reference pressurePL1. The first reference pressure PL1 is lower than the allowablepressure Pu of the refrigeration-facility units (60) (PL1<Pu). The firstreference pressure PL1 of the present embodiment is 4.5 MPa.

In the process performed in step ST1, if the value Pk measured by therefrigerant pressure sensor (48) is less than or equal to the firstreference pressure PL1 (Pk<PL1), the hydraulic pressure controller (85)performs a process in step ST2. On the other hand, if the value Pkmeasured by the refrigerant pressure sensor (48) exceeds the firstreference pressure PL1 (Pk>PL1), the hydraulic pressure controller (85)performs a process in step ST3.

In the process performed in step ST2, the hydraulic pressure controller(85) makes the first valve (18) fully open. In other words, in theprocess performed in step ST2, the hydraulic pressure controller (85)sets the opening degree of the first valve (18) at a maximum value.

In the process performed in step ST3, the hydraulic pressure controller(85) compares the value Pk measured by the refrigerant pressure sensor(48) with a second reference pressure PL2. The second reference pressurePL2 is lower than the allowable pressure Pu of therefrigeration-facility units (60), and is higher than the firstreference pressure PL1 (PL1<PL2<Pu). The second reference pressure PL2of the present embodiment is 5.2 MPa.

In the process performed in step ST3, if the value Pk measured by therefrigerant pressure sensor (48) is greater than or equal to the secondreference pressure PL2 (PL2<Pk), the hydraulic pressure controller (85)performs a process in step ST4. On the other hand, if the value Pkmeasured by the refrigerant pressure sensor (48) falls below the secondreference pressure PL2 (Pk<PL2), the hydraulic pressure controller (85)performs a process in step ST5.

In the process performed in step ST4, the hydraulic pressure controller(85) makes the first valve (18) fully closed. In other words, in theprocess performed in step ST4, the hydraulic pressure controller (85)sets the opening degree of the first valve (18) to be substantiallyzero.

In the process performed in step ST5, the hydraulic pressure controller(85) adjusts the opening degree of the first valve (18) in accordancewith the value Pk measured by the refrigerant pressure sensor (48).Specifically, the hydraulic pressure controller (85) performsproportional-integral-derivation (PID) control to adjust the openingdegree of the first valve (18) so that the value Pk measured by therefrigerant pressure sensor (48) becomes equal to a third referencepressure PL3. The third reference pressure PL3 is greater than the firstreference pressure PL1, and is less than the second reference pressurePL2 (PL1<PL3<PL2). The third reference pressure PL3 of the presentembodiment is 4.8 MPa. Note that the hydraulic pressure controller (85)may adjust the opening degree of the first valve (18) using a controlsystem except the PID control.

As described above, the hydraulic pressure controller (85) adjusts theopening degree of the first valve (18) so that the value Pk measured bythe refrigerant pressure sensor (48) becomes less than or equal to thesecond reference pressure PL2. As a result, the pressure of therefrigerant to be supplied through the second liquid connection pipe (4)from the intermediate unit (80) to the refrigeration-facility units (60)in the active state is kept below the allowable pressure Pu of therefrigeration-facility units (60).

<Control of Second Valve>

An operation performed by the hydraulic pressure controller (85) tocontrol the opening degree of the second valve (19) will be describedwith reference to FIG. 7.

The hydraulic pressure controller (85) reads the value Pk measured bythe refrigerant pressure sensor (48) at predetermined time intervals(e.g., one second). The hydraulic pressure controller (85) sets theopening degree of the second valve (19) in accordance with the value Pkmeasured by the refrigerant pressure sensor (48).

If the value Pk measured by the refrigerant pressure sensor (48) is lessthan a fourth reference pressure PL4 (Pk<PL4), the hydraulic pressurecontroller (85) makes the second valve (19) fully closed. In otherwords, in this case, the hydraulic pressure controller (85) sets theopening degree of the second valve (19) to be substantially zero. Thefourth reference pressure PL4 is greater than the second referencepressure PL2, and is less than the allowable pressure Pu (PL2<PL4<Pu).The fourth reference pressure PL4 of the present embodiment is 5.4 MPa.

If the value Pk measured by the refrigerant pressure sensor (48) isgreater than or equal to a fifth reference pressure PL5 (PL5<Pk), thehydraulic pressure controller (85) makes the second valve (19) fullyopen. In other words, in this case, the hydraulic pressure controller(85) sets the opening degree of the second valve (19) at a maximumvalue. The fifth reference pressure PL5 is greater than the fourthreference pressure PL4, and is less than the allowable pressure Pu(PL4<PL5<Pu). The fifth reference pressure PL5 of the present embodimentis 5.8 MPa.

If the value Pk measured by the refrigerant pressure sensor (48) isgreater than or equal to the fourth reference pressure PL4 and less thanor equal to the fifth reference pressure PL5 (PL4 Pk PL5), the hydraulicpressure controller (85) sets the opening degree of the second valve(19) to be a value proportional to the value Pk measured by therefrigerant pressure sensor (48).

Specifically, the hydraulic pressure controller (85) sets the openingdegree of the second valve (19) to be a value proportional to thedifference between the value Pk measured by the refrigerant pressuresensor (48) and the fourth reference pressure PL4 (Pk−PL4). If the valuePk measured by the refrigerant pressure sensor (48) is equal to thefourth reference pressure PL4 (Pk=PL4), the hydraulic pressurecontroller (85) sets the opening degree of the second valve (19) to besubstantially zero. On the other hand, if the value Pk measured by therefrigerant pressure sensor (48) is equal to the fifth referencepressure PL5 (Pk=PL5), the hydraulic pressure controller (85) sets theopening degree of the second valve (19) at a maximum value.

As described above, if the value Pk measured by the refrigerant pressuresensor (48) is greater than or equal to the second reference pressurePL2 (PL2<Pk), the hydraulic pressure controller (85) makes the firstvalve (18) fully closed. The fourth reference pressure PL4 is higherthan the second reference pressure PL2 (PL2<PL4). Thus, if the value Pkmeasured by the refrigerant pressure sensor (48) is greater than thesecond reference pressure PL2 even with the first valve (18) closed, thehydraulic pressure controller (85) opens the second valve (19).

—Refrigerant Pressure Acting on Refrigeration-Facility Expansion Valveof Refrigeration-Facility Unit—

If the refrigeration-facility units (60) are in the active state, thehydraulic pressure controller (85) adjusts the opening degree of thefirst valve (18) so that the value Pk measured by the refrigerantpressure sensor (48) becomes less than or equal to the second referencepressure PL2. Thus, if the refrigeration-facility units (60) are in theactive state, the refrigerant pressure acting on therefrigeration-facility expansion valves (63) is kept below the allowablepressure Pu of the refrigeration-facility units (60).

On the other hand, if the temperature of the inside air falls within aset temperature range, the associated refrigeration-facility controller(103) closes the associated refrigeration-facility expansion valve (63)to change the state of the associated refrigeration-facility unit (60)from the active state to the cooling-suspended state. If all of therefrigeration-facility units (60) are in the cooling-suspended state,the refrigerant pressure in the second liquid-side trunk pipe (4 b) andthe liquid-side branch pipes (4 c) increases. As a result, the value Pkmeasured by the refrigerant pressure sensor (48) increases. If the valuePk measured by the refrigerant pressure sensor (48) then increases to avalue greater than or equal to the second reference pressure PL2, thehydraulic pressure controller (85) closes the first valve (18).

As can be seen, if all of the refrigeration-facility units (60) are inthe cooling-suspended state, the refrigeration-facility expansion valves(63) of all of the refrigeration-facility units (60) and the first valve(18) of the intermediate unit (80) are closed. In this state, a portionof the refrigerant circuit (6) between the refrigeration-facilityexpansion valves (63) and the first valve (18) (the portion indicated bythe thick line in FIG. 5) encloses the refrigerant. If the temperaturesaround the second liquid-side trunk pipe (4 b) and the liquid-sidebranch pipes (4 c) are relatively high, the pressure of the refrigerantenclosed in the portion of the refrigerant circuit (6) between therefrigeration-facility expansion valves (63) and the first valve (18)(the portion indicated by the thick line in FIG. 5) increases. This maycause the refrigerant pressure acting on the refrigeration-facilityexpansion valves (63) to exceed the allowable pressure Pu of therefrigeration-facility units (60) unless some countermeasure is taken.

To address this problem, the hydraulic pressure controller (85) of theintermediate unit (80) of the present embodiment controls the openingdegree of the second valve (19). Specifically, if the value Pk measuredby the refrigerant pressure sensor (48) exceeds the fourth referencepressure PL4, the hydraulic pressure controller (85) opens the secondvalve (19). The open second valve (19) allows a portion of therefrigerant present in the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) to flow through the joint pipe (83) tothe gas-side pipe (82) and the gas connection pipe (5). As a result, therefrigerant pressure in the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) decreases.

As can be seen, in the refrigeration apparatus (1) including theintermediate unit (80) of the present embodiment, even if all of therefrigeration-facility units (60) are in the cooling-suspended state,the refrigerant pressure acting on the refrigeration-facility expansionvalves (63) of the refrigeration-facility units (60) is kept below theallowable pressure Pu of the refrigeration-facility units (60).

Here, in principle, the second valve (19) opens when all of therefrigeration-facility units (60) are in the cooling-suspended state andthe second compressor (22) is stopped. If the second valve (19) opensduring operations of the first and third compressors (21) and (23), therefrigerant present in the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) is drawn by the first compressor (21).Specifically, the refrigerant present in the second liquid-side trunkpipe (4 b) and the liquid-side branch pipes (4 c) flows through thejoint pipe (83), the gas-side pipe (82), and the gas connection pipe (5)in this order into the outdoor circuit (11), and joins the refrigerantdischarged from the third compressor (23) after passing through thesecond bypass pipe (24 b). The resultant refrigerant is subsequentlysucked into the first compressor (21) after passing through theintercooler (17).

In some cases, the hydraulic controller (85) opens the second valve (19)while all of the compressors (21, 22, 23) are stopped. In such a case,the first compressor (21) may be started, and the refrigerant present inthe second liquid-side trunk pipe (4 b) and the liquid-side branch pipes(4 c) may be drawn into the first compressor (21). This causes therefrigerant present in the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) to turn into the form of single-phase gaswhile passing through the intercooler (17), and to be then sucked intothe first compressor (21).

—Feature (1) of Embodiment—

The intermediate unit (80) of the present embodiment is provided betweenthe heat source unit (10) and the refrigeration-facility units (60),which are connected together through the liquid connection pipe (4) andthe gas connection pipe (5) to form part of the refrigeration apparatus(1). The intermediate unit (80) includes the liquid-side pipe (81), thefirst valve (18), the refrigerant pressure sensor (48), and thehydraulic pressure controller (85). The liquid-side pipe (81) isconnected to the liquid connection pipe (4). The first valve (18) is avalve provided for the liquid-side pipe (81) and having a variableopening degree. The refrigerant pressure sensor (48) is disposed in aportion of the liquid-side pipe (81) closer to therefrigeration-facility units (60) than the first valve (18) is, andmeasures the pressure of the refrigerant flowing through the liquid-sidepipe (81). The hydraulic pressure controller (85) adjusts the openingdegree of the first valve (18) based on the value measured by therefrigerant pressure sensor (48).

In the refrigeration apparatus (1) of the present embodiment, therefrigerant sent out from the heat source unit (10) and flowing throughthe liquid connection pipe (4) is supplied to the refrigeration-facilityunits (60) after passing through the liquid-side pipe (81) of theintermediate unit (80). The hydraulic pressure controller (85) changingthe opening degree of the first valve (18) for the liquid-side pipe (81)triggers a change in the pressure of the refrigerant that has passedthrough the first valve (18). The hydraulic pressure controller (85)changing the opening degree of the first valve (18) based on the valuemeasured by the refrigerant pressure sensor (48) triggers a change inthe pressure of the refrigerant to be sent from the intermediate unit(80) to the refrigeration-facility units (60).

In the refrigeration apparatus (1) of the present embodiment, theintermediate unit (80) adjusts the pressure of the refrigerant flowinginto the refrigeration-facility units (60). For this reason, even if theheat source unit (10) does not perform control with consideration givento the allowable pressure of the refrigeration-facility units (60), therefrigeration-facility units (60) having an allowable pressure that islower than that of the heat source unit (10) can be connected to theheat source unit (10). Thus, according to the present embodiment,various models of refrigeration-facility units can be connected to theheat source unit (10) without complicating the manner of controlperformed by the heat source unit (10).

—Feature (2) of Embodiment—

The intermediate unit (80) of the present embodiment includes thegas-side pipe (82), the joint pipe (83), and the second valve (19). Thegas-side pipe (82) is connected to the gas connection pipe (5). Thejoint pipe (83) connects the portion of the liquid-side pipe (81) closerto the refrigeration-facility units (60) than the first valve (18) isand the gas-side pipe (82) together. The second valve (19) is providedfor the joint pipe (83).

Here, while the refrigeration-facility expansion valves (63) of therefrigeration-facility units (60) and the first valve (18) of theintermediate unit (80) are all closed, the refrigerant is enclosed in aportion of the liquid connection pipe (4) between the intermediate unit(80) and the refrigeration-facility units (60). If this state occurswhile the air temperature around the liquid connection pipe (4) is high,the internal pressure of the liquid connection pipe (4) increases. Thismay damage the refrigeration-facility units (60).

To address this problem, the intermediate unit (80) of the presentembodiment includes the joint pipe (83) connecting the liquid-side pipe(81) and the gas-side pipe (82) together and provided with the secondvalve (19). While the second valve (19) is open, the portion of theliquid connection pipe (4) between the intermediate unit (80) and therefrigeration-facility units (60) communicates with the gas connectionpipe (5) via the joint pipe (83). This can substantially prevent theinternal pressure of the liquid connection pipe (4) from increasingexcessively while the refrigeration-facility expansion valves (63) ofthe refrigeration-facility units (60) and the first valve (18) of theintermediate unit (80) are all closed. As a result, therefrigeration-facility units (60) can be substantially prevented frombeing damaged.

—Feature (3) of Embodiment—

In the intermediate unit (80) of the present embodiment, the hydraulicpressure controller (85) adjusts the opening degree of the first valve(18) so that the value measured by the refrigerant pressure sensor (48)becomes less than or equal to the second reference pressure PL2. If thevalue measured by the refrigerant pressure sensor (48) exceeds “thefourth reference pressure PL4 higher than the second reference pressurePL2” even with the first valve (18) closed, the hydraulic pressurecontroller (85) opens the second valve (19).

The hydraulic pressure controller (85) of the intermediate unit (80) ofthe present embodiment controls the first and second valves (18) and(19). The hydraulic pressure controller (85) controlling the first valve(18) allows the pressure of the refrigerant that is about to be suppliedfrom the intermediate unit (80) to the refrigeration-facility units (60)to be substantially kept at or below the second reference pressure PL2.The hydraulic pressure controller (85) controlling the second valve (19)substantially prevents the internal pressure of the portion of theliquid connection pipe (4) between the intermediate unit (80) and therefrigeration-facility units (60) from increasing excessively even whilethe first valve (18) is closed.

—Feature (4) of Embodiment—

The intermediate unit (80) of the present embodiment is installedindoors, and is connected to the heat source unit (10) installedoutdoors.

The intermediate unit (80) of the present embodiment is placed indoors.Thus, in the summer when the outdoor air temperature is high, the airtemperature around the portion of the liquid connection pipe (4) betweenthe intermediate unit (80) and the refrigeration-facility units (60) islower than that outdoors. This can substantially prevent the internalpressure of the portion of the liquid connection pipe (4) between theintermediate unit (80) and the refrigeration-facility units (60) fromincreasing while the refrigeration-facility expansion valves (63) of therefrigeration-facility units (60) and the first valve (18) of theintermediate unit (80) are all closed.

The intermediate unit (80) may be arranged in the indoor space where therefrigeration-facility units (60) are also arranged. Therefrigeration-facility units (60) are typically installed in an indoorspace to be air-conditioned by an air-conditioning unit (50). Forexample, even if the outdoor air temperature is relatively high in thesummer, the air temperature in the indoor space including theintermediate unit (80) and the refrigeration-facility units (60) islower than the outdoor air temperature. Thus, the intermediate unit (80)installed indoors could substantially prevent the internal pressure ofthe portion of the liquid connection pipe (4) between the intermediateunit (80) and the refrigeration-facility units (60) from increasingwhile the refrigeration-facility expansion valves (63) of therefrigeration-facility units (60) and the first valve (18) of theintermediate unit (80) are all closed.

—Feature (5) of Embodiment—

The refrigeration apparatus (1) of the present embodiment includes theintermediate unit (80), the heat source unit (10), therefrigeration-facility units (60), the liquid connection pipe (4), andthe gas connection pipe (5). The liquid connection pipe (4) and the gasconnection pipe (5) connect the intermediate unit (80), the heat sourceunit (10), and the refrigeration-facility units (60) together to formthe refrigerant circuit (6).

In the refrigeration apparatus (1) of the present embodiment, theintermediate unit (80) is disposed between the heat source unit (10) andthe refrigeration-facility units (60) in the refrigerant circuit (6).The liquid-side pipe (81) of the intermediate unit (80) is connected tothe liquid connection pipe (4). Changing the opening degree of the firstvalve (18) of the intermediate unit (80) triggers a change in thepressure of the refrigerant to be sent through the liquid connectionpipe (4) from the intermediate unit (80) to the refrigeration-facilityunits (60).

—Feature (6) of Embodiment—

The refrigeration apparatus (1) of the present embodiment includes theintermediate unit (80), the heat source unit (10), therefrigeration-facility units (60), the liquid connection pipe (4), andthe gas connection pipe (5). The liquid connection pipe (4) includes theliquid-side trunk pipes (4 a, 4 b) connected to the heat source unit(10), and the plurality of liquid-side branch pipes (4 c) eachconnecting an associated one of the refrigeration-facility units (60) tothe liquid-side trunk pipes (4 a, 4 b). The gas connection pipe (5)includes the gas-side trunk pipes (5 a, 5 b) connected to the heatsource unit (10), and the plurality of gas-side branch pipes (5 c) eachconnecting an associated one of the refrigeration-facility units (60) tothe gas-side trunk pipes (5 a, 5 b). The liquid-side pipe (81) of theintermediate unit (80) is connected to the liquid-side trunk pipes (4 a,4 b) of the liquid connection pipe (4). The gas-side pipe (82) of theintermediate unit (80) is connected to the gas-side trunk pipes (5 a, 5b) of the gas connection pipe (5).

In the refrigeration apparatus (1) of the present embodiment, theplurality of refrigeration-facility units (60) are connected through theliquid connection pipe (4) and the gas connection pipe (5) to the heatsource unit (10). The intermediate unit (80) is connected to theliquid-side trunk pipes (4 a, 4 b) of the liquid connection pipe (4) andthe gas-side trunk pipes (5 a, 5 b) of the gas connection pipe (5). Therefrigerant that has flowed from the heat source unit (10) into theliquid-side trunk pipes (4 a, 4 b) of the liquid connection pipe (4)passes through the first valve (18) of the intermediate unit (80), andis then distributed among the plurality of refrigeration-facility units(60).

—First Variation of Embodiment—

The second valve (19) of the intermediate unit (80) of the foregoingembodiment may be an on-off valve that selectively switches between thefully-closed state and the fully-open state. A second valve (19) of thisvariation is an electromagnetic valve including a solenoid that drivesits valve body.

As shown in FIG. 8, when the second valve (19) is in the fully-closedstate, and the value Pk measured by the refrigerant pressure sensor (48)reaches the fifth reference pressure PL5 (Pk=PL5), a hydraulic pressurecontroller (85) of this variation changes the state of the second valve(19) from the fully-closed state to the fully-open state. When thesecond valve (19) is in the fully-open state, and the value Pk measuredby the refrigerant pressure sensor (48) reaches the fourth referencepressure PL4 (Pk=PL4), the hydraulic pressure controller (85) of thisvariation changes the state of the second valve (19) from the fully-openstate to the fully-closed state. The fourth and fifth referencepressures PL4 and PL5 are respectively equal to those set when thesecond valve (19) is a control valve having a variable opening degree.

—Second Variation of Embodiment—

The hydraulic pressure controller (85) of the foregoing embodiment mayset the fourth reference pressure PL4 at a value slightly less than thesecond reference pressure PL2 (PL4<PL2). Even in such a case, the fourthreference pressure PL4 is set at a value greater than the firstreference pressure PL1 (PL1<PL4). It is possible for a second valve (19)of an intermediate unit (80) of this variation to start opening beforethe first valve (18) falls into the fully-closed state.

—Third Variation of Embodiment—

The intermediate unit (80) of the foregoing embodiment may include apressure input section (86). The pressure input section (86) is a memberto be operated by an operator to input information on the allowablepressure Pu of the refrigeration-facility units (60) to the hydraulicpressure controller (85). Examples of the pressure input section (86)include a DIP switch and a numeric keypad for input of numerals.

As shown in FIG. 9, a pressure input section (86) of an intermediateunit (80) of this variation is electrically connected to a hydraulicpressure controller (85) via a communication line or any other similarelement. Information input to the pressure input section (86) istransmitted to the hydraulic pressure controller (85), and is recordedin a memory device of the hydraulic pressure controller (85).Information to be input to the pressure input section (86) may includethe allowable pressure Pu of the refrigeration-facility units (60) or asymbol such as a number corresponding to the allowable pressure Pu.

The hydraulic pressure controller (85) of this variation sets thereference pressures PL1 to PL5 based on the information input to thepressure input section (86), and controls the opening degrees of thefirst and second valves (18) and (19) with reference to the setreference pressures PL1 to PL5.

—Fourth Variation of Embodiment—

The intermediate unit (80) of the foregoing embodiment may omit thegas-side pipe (82), the joint pipe (83), and the second valve (19). Forexample, if the refrigeration apparatus (1) is installed in a coldclimate area where the air temperature in the summer is not so high, therefrigerant pressure in the second liquid-side trunk pipe (4 b) and theliquid-side branch pipes (4 c) may be kept at or below the allowablepressure of the refrigeration-facility units (60) even with therefrigeration-facility expansion valves (63) of all of therefrigeration-facility units (60) and the first valve (18) of theintermediate unit (80) closed. Thus, the intermediate unit (80) formingpart of the refrigeration apparatus (1) installed in the cold climatearea may omit the gas-side pipe (82), the joint pipe (83), and thesecond valve (19). An intermediate unit (80) of this variation isconnected only to a liquid connection pipe (4) but is not connected to agas connection pipe (5).

—Fifth Variation of Embodiment—

The refrigeration apparatus (1) of the foregoing embodiment may omit theair-conditioning units (50) while including the heat source unit (10)and the refrigeration-facility units (60). A refrigeration apparatus (1)of this variation exclusively cools inside air. A heat source unit (10)forming part of the refrigeration apparatus (1) of this variation omitsa third compressor (23).

—Sixth Variation of Embodiment—

The utilization units of the refrigeration apparatus (1) of theforegoing embodiment are not limited to the air-conditioning units (50)configured to condition air in a room. The utilization units of therefrigeration apparatus (1) of the foregoing embodiment may beconfigured to heat or cool water using a refrigerant. A utilization unitof this variation includes a heat exchanger configured to exchange heatbetween a refrigerant and water, as a utilization heat exchanger.

While the embodiment and variations thereof have been described above,it will be understood that various changes in form and details may bemade without departing from the spirit and scope of the claims. Theembodiment and the variations thereof may be combined and replaced witheach other without deteriorating intended functions of the presentdisclosure.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing description, the present disclosure isuseful for an intermediate unit for a refrigeration apparatus, and arefrigeration apparatus including the intermediate unit.

EXPLANATION OF REFERENCES

-   1 Refrigeration Apparatus-   4 Liquid Connection Pipe-   4 a First Liquid-Side Trunk Pipe-   4 b Second Liquid-Side Trunk Pipe-   4 c Liquid-Side Branch Pipe-   5 Gas Connection Pipe-   5 a First Gas-Side Trunk Pipe-   5 b Second Gas-Side Trunk Pipe-   5 c Gas-Side Branch Pipe-   10 Heat Source Unit-   18 First Valve-   19 Second Valve-   48 Refrigerant Pressure Sensor-   60 Refrigeration-Facility Unit (Utilization Unit)-   80 Intermediate Unit-   81 Liquid-Side Pipe-   82 Gas-Side Pipe-   83 Joint Pipe-   85 Hydraulic Pressure Controller (Controller)

1. An intermediate unit for a refrigeration apparatus, the intermediateunit being provided between a heat source unit and a utilization unit,the heat source unit and the utilization unit being connected togetherthrough a liquid connection pipe and a gas connection pipe to form therefrigeration apparatus, the intermediate unit comprising: a liquid-sidepipe connected to the liquid connection pipe; a first valve provided forthe liquid-side pipe, the first valve having a variable opening degree;a refrigerant pressure sensor disposed in a portion of the liquid-sidepipe closer to the utilization unit than the first valve is, therefrigerant pressure sensor being configured to measure a pressure of arefrigerant flowing through the liquid-side pipe; and a controllerconfigured to adjust the opening degree of the first valve based on avalue measured by the refrigerant pressure sensor.
 2. The intermediateunit of claim 1 further comprising: a gas-side pipe connected to the gasconnection pipe; a joint pipe connecting the portion of the liquid-sidepipe closer to the utilization unit than the first valve is and thegas-side pipe together; and a second valve provided for the joint pipe.3. The intermediate unit of claim 2, wherein the controller adjusts theopening degree of the first valve so that the value measured by therefrigerant pressure sensor is less than or equal to a referencepressure, and opens the second valve if the value measured by therefrigerant pressure sensor is greater than the reference pressure withthe first valve closed.
 4. The intermediate unit of claim 1, wherein theintermediate unit is installed indoors, and is connected to the heatsource unit installed outdoors.
 5. A refrigeration apparatus,comprising: the intermediate unit of claim 1; a heat source unit; autilization unit; and a liquid connection pipe and a gas connection pipeconnecting the intermediate unit, the heat source unit, and theutilization unit together to form a refrigerant circuit.
 6. Arefrigeration apparatus, comprising: the intermediate unit of claim 2; aheat source unit; a plurality of utilization units; a liquid connectionpipe including a liquid-side trunk pipe and a plurality of liquid-sidebranch pipes, the liquid-side trunk pipe being connected to the heatsource unit, the liquid-side branch pipes each connecting an associatedone of the utilization units to the liquid-side trunk pipe; and a gasconnection pipe including a gas-side trunk pipe and a plurality ofgas-side branch pipes, the gas-side trunk pipe being connected to theheat source unit, the gas-side branch pipes each connecting anassociated one of the utilization units to the gas-side trunk pipe, theliquid-side pipe of the intermediate unit being connected to theliquid-side trunk pipe of the liquid connection pipe, the gas-side pipeof the intermediate unit being connected to the gas-side trunk pipe ofthe gas connection pipe.